The technology described herein relates to antennas, and in particular to radio antennas for communicating with mobile radios.
Mobile radio antennas for mobile radio base stations are generally provided with a number of radiating element arrangements, located one above the other in the vertical direction, in front of a reflector plane. These radiating element arrangements may comprise a large number of dipole radiating elements. Such dipole elements may for example be in the form of crucible dipoles, a dipole square, or other radiating element types which have a dipole structure. Antennas in the form of so-called patch radiating elements are also known.
As is known, mobile radios can operate on various mobile radio frequency bands. For example, the 900 MHz frequency band is generally used for the so-called GSM 900 network; and the 1800 MHz or the 1900 MHz frequency band are used for the so-called GSM 1800 network in the USA and in a large number of other countries. A frequency band around 2000 MHz has been allocated for the next mobile radio generation, namely the UMTS network.
It is thus usual to design mobile radio antennas as at least dual-band antennas. Triple-band antennas may also be desirable (for example, for the 900 MHz, for the 1800 and 1900 MHz or, for example, for the 2000 MHz band).
Furthermore, such mobile antennas are preferably designed as dual-polarized antennas for operation with polarizations of +45xc2x0 and xe2x88x9245xc2x0. It is also usual for such antennas to be protected against weather influences by a plastic shroud. This so-called radome has to achieve objects which are primarily mechanical and surrounds all the radiating antenna parts to the same extent. An antenna such as this for operation in at least two frequency bands that are offset with respect to one another has been disclosed, by way of example, in DE 198 23 749 A1 corresponding to U.S. Pat. No. 6,333,720 owned by the present assignee.
One problem that frequently arises with such two-band or multiband antennas in general is that the 3 dB beam widths of the polar diagram in the azimuth direction may differ widely for the different frequency ranges and/or bands. A further problem that often occurs with two-band or multiband antennas is that cross-polar components can lead to deterioration in the polar diagram characteristic. The VSWR ratio and/or the decoupling may also be disadvantageously influenced.
Many known antennas in the prior art are designed for only a single frequency bandxe2x80x94that is, they can receive and transmit in only one frequency band. These may be linear-polarized or dual-polarized antennas for transmission in only one frequency band. Antennas such as these which operate in only one frequency band are disclosed, for example, in the publications DE 199 01 179 A1, DE 198 21 223 A1, DE 196 27 015 C2, U.S. Pat. No. 6,069,590 A and U.S. Pat. No. 6,069,586 A. These prior publications generally deal with different types of problems including decoupling two polarizations in the same frequency band. Electrically conductive parts are generally used for this purpose, to produce decoupling elements that radiate parasitically.
Exemplary non-limiting technology described herein provides a considerable improvement (irrespective of whether the antenna is operated with only one polarization or with a number of polarizations), at least for operation in two frequency bands, with regard to the 3 dB beam width and/or with regard to the suppression of the cross-polar component and/or of the VSWR ratio and/or with regard to decoupling and increasing the bandwidth.
The advantages mentioned above are obtained not just individually but also cumulatively by exemplary illustrative technology described herein
Providing a dielectric body for a mobile radio antenna is known per se, which dielectric body has at least one extent direction parallel to the reflector plane that is larger than its extent component which runs at right angles to the reflector plane. However, the dielectric body according to exemplary non-limiting implementations herein is preferably in the form of a plate. In particular, in a plan view, it may be in the form of an n-sided polygon, and may extend, for example, above a dipole radiating element arrangement, for example a cruciform dipole, a dipole square or a patch radiating element, with the extent position being located above the corresponding radiating elements for a higher frequency band and below the radiating elements at least for the lowest frequency band.
Furthermore, the dielectric body according to exemplary non-limiting implementations, (which is also referred to as a dielectric tuning plate in places in the following text) is symmetrical when seen in a plan view, and may have at least sections which are designed to be and are arranged symmetrically with respect to an individual radiating element arrangement.
Furthermore, it has also been found to be advantageous, in addition or alternatively, to arrange corresponding dielectric bodies at a distance in front of the reflector plate, between two radiating element arrangements which are generally arranged located one above the other in the vertical direction in front of a vertical reflector plane.
The dielectric bodies according to exemplary non-limiting implementations may, for example, be composed of suitable plastic material, for example polystyrene, glass fiber reinforced plastic (GFRP), etc.
A material whose dielectric does not have a high loss factor is preferably used for the dielectric body in exemplary illustrative implementations.
An exemplary non-limiting implementation has a particularly advantageous effect, for example, in the frequency bands from 800 to 1000 MHz and from 1700 to 2200 MHz.
The dielectric body is preferably in the form of a plate and extends in a parallel plane in front of the reflector. However, it may also be provided with attachment devices or stand feet (in general spacers etc.) which are composed of the same material, in order to arrange it at a predetermined distance, which has been found to be advantageous, in front of the reflector plate. The extent height is preferably less than xcex/2.
The antenna according to exemplary non-limiting implementations makes it possible to achieve a considerable reduction in the frequency dependency of the 3 dB beam width. Mobile radio antennas are frequently set such that they have a 3 dB beam width of 65xc2x0. This 65xc2x0 3 dB beam width can, however, normally not be set completely identically for the at least two frequency bands, particularly if these are very broad bands. A discrepancy with regard to the at least two intended frequency bands of, for example, 65xc2x0xc2x110xc2x0 (or at least xc2x17xc2x0) is typical in the prior art. According to exemplary non-limiting implementations described herein, this discrepancy can now be improved to 65xc2x0xc2x15xc2x0 (or even only xc2x14xc2x0 or less).
As is known, antennas for use in communicating with mobile radios, are frequently adjusted such that they each emit in a horizontal 120xc2x0 sector angle. This is also referred to as a sector. Three sectors are thus formed per stationary antenna mast. A corresponding mobile radio antenna thus transmits at an angle of +60xc2x0 or xe2x88x9260xc2x0 at the sector boundaries, with the suppression of the cross-polar components, especially at the sector boundaries according to the prior art, having poor values, particularly in the case of broadband antennas. The antenna according to exemplary non-limiting implementations herein using the dielectric tuning body can allow a ratio of 10 dB or even better to be achieved, even at the sector boundaries at xc2x160xc2x0, with regard to the suppression of the cross-polar component.
Ifxe2x80x94although this is not essentialxe2x80x94cross-polarizing radiating elements are used in a multiband (e.g., at least dual band) antenna arrangement, then the decoupling can likewise be improved considerably. The required decoupling is in the order of magnitude of more than 30 dB. This can be a major problem, particularly in the case of broadband antennas or antennas with an electrically adjustable notch. The antenna according to exemplary non-limiting implementations herein considerably exceeds this valuexe2x80x94in particular even when the antennas have a broad bandwidth and are also electrically adjustable.
A further positive factor is bandwidth broadening, especially for the higher frequencies.
Advantages mentioned above with the dielectric body according to exemplary non-limiting implementations have a positive effect especially for higher frequency bands, with the measures having virtually no influence on lower or lowest intended frequency bands.